Aviation future

In another thread we talked about converting to a durable economy that is not dependent on fossil fuel. Now flexibility on energy and mobility seem to be inverse proportional. In static plants you can use anything that's available. Cars are more limited although there is still a range of possible energy sources (gaz, gaseous, electrical). Aviation however seems to be fully dependent on liquid fuel.

Some remarks:

How are we going to continue to sustain Jumbo-jets and Air-busses with fuel. Synthetic fuels? Perhaps but any idea how much jet - air fuel A1 is consumed every second?

I see some 300-500 Airlines continuoisly airborne over Europe. That may amout to 1500 - 2000 worldwide perhaps? Average fuel consumption some 9000 liters per hour, say 3 liters per airliner per second. How are we going to produce 6000 minimum liters (1600 gallons) of synthetic fuel per second?

Aviation is an intrinsic part of the economy and booming business
-Aircraft propulsion is dependable on liquid fuel and lots of it.
-Liquid fuel in massive amounts is only available from fossil origine
-If that's no longer economical feasible what are we going to burn in the planes?
-A synthetic liquid fuel (alcohol?) may not be producable at the required rate.
So we need to think about something else and fast, since jets take a decade or so to devellop and three decades to mature and we don't know how much time we have.

Soving this issue seems to be an essential mission and the first to do that has excellent chances for a lead position in the future.

In terms of propulsion, the alternative fuel sources just are not there yet. So the direction has been and will be for quite some time, to get lighter and more efficient. The next big thing is the use of ceramics into what used to be metallic components. New sweep designs for blades is also helping the overall efficiencies. As far as synthetic fuels are concerned, the price per gallon is definitely cost prohibitive at this point.

Maybe the problem is that people "have" to be at certain places
at certain times, that is what guzzles un renewable fuel, in the years
before aviation sailing vessels took months to reach there destination,
so is it not our lifestyle becoming more and more hectic that is at
fault, so chill out and catch the next Super blimp and allow an extra
couple of days to your business, holiday trip.

Maybe what we need to do is start by converting the easier stuff over to alternative energy sources. Thereby leaving more fossil fuels for the less easily convertible vehicles. Then perhaps as the alternative fuel/energy technology becomes more developed it becomes cheaper, more versatile and then gets implemented on the harder to convert stuff.

I think in terms of propulsion the only alternative for fighter jets and supersonics and space shuttles would be EM-based 'miracle' of some sort.

As far as petrochemical industry is concerned - they'll never go away. Oil is a hydrocarbon and we need oil to simply survive and sustain our organic heritage. From drugs to foods to nylon to polymers - we need the benzin rings and aromatics and the whole nine yards.

For big aviation - jumbo jets and so on - the alternative might become bubble-based fusion propeller-driven system. Its never going to be supersonic, but then again I dont think I'd want to fly supersonic in a jumbo jet.. its just never going to be safe. Going at 0.8 M is good enough for almost anyone.

Another alternative is hydrogen fuel.. this would be the best alternative since most of the universe is hydrogen.. and if we run out of it we can always "make more" through nuclear means.

Aviation is just like anything else in this world. It is driven by the economy. The nanosecond it becomes cost prohibitive to do something one way, it gets changed. Plain and simple. Until this, what I call fictious, day of "peak oil" arrives, small steps will continue to happen like they are now.

i definately see the materials of the aircraft changing. Carbon fiber, new alloys, ceramics.

Now bear in mind that the plane is already developed. But back in the day (1911?) planes were just made, think of long it took to make them commerically useful and how much time was spent prior on fool's errands that never worked.

If the next energy source will fit in a plane, then fine. But something tells me we will have to wait for new technologies to go with the new propulsion systems.

Aviation fuel is 1% of consumption. Fuel is 14% of airline costs. And, in Europe, the tax portion of fuel is a big part of the total cost, so prices don't fluxuate as rapidly in response to oil price hikes. An increase of oil prices from the current $50 a barrel to $400 a barrel would double the cost of an airline ticket. (By comparison, a passenger car now costs about $20,000 for a midrange model with lifetime fuel costs of ca. $10,000 at $2 a gallon, but at $16 a gallon, the car would still cost $20,000, but the fuel would cost $80,000, increasing the total cost of driving a car three fold plus, with an even bigger impact for freight trucks). Business travel and the rich leisure traveler would absorb this (and perhaps put up with coach class seating). Leisure travel by the middle class would fall off.

There would be far more impact in freight and leisure traffic, which would switch to far more fuel efficient rail and seaborn approaches for medium and long haul distances, and could use electric vehicles (which don't make sense now, but would if oil prices went up eight fold) for local transporation (they perform equally well, but cost a bit more for the vehicle (maybe 50%) which would come down in mass production-- fuel is already cheaper-- and they have limited range ca. 80-120 miles, which is fine for short haul trips).

If oil was gone, biofuels could replace the entire demand of the aviation sector which would be somewhat smaller that the current aviation sector at those prices. (Indeed, as long as oil became more expensive than biofuels, biofuels would replace mineral oil entirely). Rape seed oil can't easily supply all current fossil fuel demands, but it could meet the aviation sector's demands which are so small compared to total oil demand.

Note also, that it doesn't even matter if biofuels are negative energy products (as critics, probably incorrectly, claim). The point of using biofuels for aviation is to convert energy you can easily produce with alternatives for electricity, into a liquid fuel that doesn't have good alternatives.

Of course, there would also be more of an incentive to make planes more fuel efficient per passenger, if prices went up. Sending your luggage ahead by rail, for instance, while you fly, would probably become more common, in addition to more cramped business class seating.

The key to fuel is "available energy per unit mass" of the fuel itself and of the chemcial-to-mechanical conversion system. That makes it hard to replace current fossil fuel based aviation with alternatives.

Solar Powered aircraft and terrestrial vehicles have been developed. However the specific energy of such systems is low compared to fossil fuel systems.

In fixed power plants, mass is not so much an issue. One does not worry about moving the fixed mass. Mass is a technical and economic constraint in propulsive systems.

As for fossil fuel based propulsive systems (alternatives are discussed in another thread), a by-product of the hydrogen economy would be continued, but limited reliability on fossil fuels. http://www.ecn.nl/biomassa/research/poly/ftsynthesis.en.html [Broken] is one possiblity to recycle CO2. Of course, economics will dictate how this would be implemented.

I'd say we stop using liquid fossile fuel down on the ground, and leaves it to the aviation business instead, if we can come up with good, convenient alternatives.

When it comes to saving fuel in the aviation business I'd introduce propeller-driven stirling-powered airliners. Not everybody needs to go at Mach .8 all the time. And this might also open up for more comfort instead. Plus, a stirling could burn Jet fuel, just like a turboprop or jet, only being more efficient, especially at altitude, with the increased temperature delta in the cold air.

Also, how feasable is it to power an axial compressor using a well-balanced stirling? Could this make a new efficient jet-like design? Kind of how recip engines power jetskis.

Propellor driven is a bad idea. You cannot go as high, meaning that your max altitude, where it is best for fuel economy, is in areas of high turbulence. Jet engines can fly higher than any propellor. It is the inherent nature of the two, no matter the fuel being used.

It also represents a step backward in aviation technology, and you will see the downfall of the industry if you try to use props again.

With 3.5 times more energy per kg than jet fuel, liquid hydrogen should be the perfect aviation fuel, and likely very soon will be given recent steep increases in petroleum. Only remains to come up with an economic source, although already a couple of methods of production are very close to competing on a Joule/$ basis. An aircraft is an ideal use of liquid hydrogen fuel (much better than autos) as it is easy to plan it's refueling on a schedule which enables total fuel use without any need to vent gas to cool the tanks. (eg. only problem with venting vapour from liquid H2 tanks in autos is after 2 days of not running which rarely if ever happens to an aircraft). And with modern composites, designing safe lightweight low pressure cryo-tanks should only be a matter of someone requesting it.

My concern about liquid hydrogen as aviation fuel would be the impact of the fuel tanks. The tanks would be larger and a larger share of the total fuel and fuel storage system mass than current aviation fuels, and would reduce the effective energy/mass ratios from the theoretical maximum by quite a bit.

Also, I would suspect that producing liquid hydrogen from a non-fossil fuel source (like electrolisis) would be significantly more expensive than making a biofuel based aviation fuel, and simply liquifying hydrogen using current technology is quite energy intensive.

However, while hydrogen offers many benefits, there are two drawbacks to using it as a fuel with current technology. Liquid hydrogen, the preferred form of hydrogen, requires four times the storage space of conventional petroleum-based fuels. The other problem is that hydrogen production depends on the availability of a nonrenewable resource, petroleum. Currently, hydrogen is produced from raw petroleum for industrial use, but petroleum supplies may become limited in the near future.

[snip]

The major advantage is that hydrogen stores approximately 2.8 times the energy per unit mass as gasoline. The disadvantage is that it needs four times the volume for a given amount of energy. For example, a 15-gallon tank of gasoline contains 90 pounds of gasoline; a 60-gallon tank of gaseous hydrogen would weigh only 34 pounds. [Ed: 90/2.8=32 so both tanks would approximately equal energy. It also appears that this example excludes the weight of the tank itself.]

Linde (1997) state that they have liquid hydrogen transportation containers available with volumetric capacities of 15,000, 41,000 and 53,000 litres. The largest container has a capacity similar to that of gasoline transportation trucks in Canada and the middle size is similar to gasoline trucks in the US. The weight of hydrogen transported, the payload, in each of these containers is only 1,000, 2,900 and 3,750 kg respectively. The payload of gasoline transported in a similar size of truck is an order of magnitude higher. The fuel that is consumed in delivering the fuel payload to the customer moves the weight of the truck both ways and the payload one way. If the weight of the truck and trailer is 40,000 kg then the liquid hydrogen payload contributes to only about 4.5% of the total fuel consumed (3,750/2*40,000 + 3,750) whereas the gasoline payload contributes to about 30% of the fuel consumed (37,500/37,500+2*40000). . . . Amos (1998) details the costs of storing and transporting hydrogen. In his transportation cost assumptions, he assumed that 4,082 kg of liquid hydrogen could be delivered by a truck and that the truck averaged 6 miles per gallon (39.4 l/100 km) for the round trip.

If hydrogen has three times as much energy per mass, but the combined fuel+tank weight for liquid hydrogen is ten times a great per kilogram of liquid hydrogen as it is per kilogram of jet fuel, then using liquid hydrogen cuts the range of your aircraft to about a third of the range of existing aircraft.

On tankage. All those quotes in your post are based on current use metal tanks which are basically derived from stationary tanks which have no need for mass ratio optimization, and show it. Eg. Chart Industries http://www.chart-ind.com/pdf/10888322.pdf However, stating something is impossible without even offering eg. Chart the opportunity to develop the optimal seems premature.

Theoretically using optimal (round cylinder) tank section and modern composites for construction of the inner pressure vessel (303 kpa x 4:1 safety) and the outer vacume vessel (202 kpa x 4:1 safety), an 80 kg allowance for fittings and instruments and a 200 kg allowance for attachments etc. , one should be able to build a 57,310 litre tank (95% fill) weighing only 715 kg.

Thats 4,000 kg of hydrogen, equivalent to 14,000 kg of jet fuel, in a 715 kg tank. Should fly, esp. since no engine supply fuel pumps would be needed and in fact the engines could theoretically benefit enormously from the huge cooling capacity of the fuel as it vapourizes itself to injection pressure. Intercooling of the compressors?

And at what point did non-fossil become a criterion? Today, the cheapest source of hydrogen is collecting it (almost free off-peak) from the gassifier sections of oxygen-blown coal-fired IGCC (Integrated Gassifier Combined Cycle) electrical generating stations. If the CO2 is a problem there, then it's easy to capture from the pure CO2 exhaust stream if you come up with a way to sequester it.

Of course Sulphur-Iodine cycle thermal separtion using nuclear heat input will also work, and likely cheaper once proven.

Airframers are very dependent on the volume of the fuel required. There's some fine points here to be considered: Airframers look at the Higher Heating Value (HHV) of a fuel for the total volume of fuel required in their application. Engine manufacturers use the Lower Heating Value (LHV) for all of their cycle performance data crunching. The difference is in the energy contained in the fuel vs. the actual energy used by the engine. When a fuel burns, some of that energy goes into the formation of water as a byproduct. For petroleum fuels it is about a 6% factor to consider. I BELIEVE hydrogen is around the 11% range (I will have to double check that). That means that the requirement of an engine would result in an 11% increase in the required volume for the airframe manufacturer.

That being said, volume is very important because it not only because of weight but because of size. A new form of composite tanks that are flight worthy (which I personally have not seen) may eliminate weight, but not size. That means wings, fuselages and supporting structures have to be larger. Plus you add the cryogenic requirements to the airframe as well. All of this has to be considered.

A study done by Airbus had one result:

A key issue was to model the liquid hydrogen fuel system architecture - per unit of energy, liquid hydrogen has four times the volume of kerosene - so fuel tanks four times as large needed to be fitted in, or on to, each aircraft category. Modelling showed that, owing to the larger exterior surface area needed to accommodate the fuel tanks; energy consumption would increase by 9% - 14%, as would the maximum take-off weight. Overall operating costs would increase by 4% to 5% due to the fuel alone.

One interesting point it made was in regards to water vapor as an exhaust emission:

However, there are minor emissions of oxides of nitrogen, and the water in the aircraft’s contrail is also a greenhouse gas at high altitudes. However the residency time of water vapour in the upper atmosphere is 6 months, whereas carbon dioxide remains in place for around 100 years.

That's a huge reduction in time, but I never knew that water vapor could be a greenhouse gas. One learns something new everyday.

The same study really had nothing bad to say about the hydrogen concept and estimated a 20-25 year timeframe for implementation. However a lot of work has to be done. It's not a simple changeover, especially when one considers how airlines operate in terms of replacing aircraft in their fleets...slowly.

In all my comparisons I was using LHV, eg. 120/34 = 3.529 . Is 34 valid for LHV jet fuel?

In general I agree with all your statements though am wary of things like 20 - 25 yr time frames and 4 - 5% increased costs because most of these studies failed to predict the recent rapid rises in cost of petroleum fuels. (Note that EERE's 2005 report is STILL projecting gasoline to cost <US$2.00/USgal. out to 2025 which IMHO is ridiculous.)